Plasma sprayed coatings (i.e., flame, arc, and other similar sprayed coatings) are commonly used in gas turbine engines and other types of turbomachinery. One reason for their widespread use is that the process for applying plasma sprayed coatings is capable of depositing a wide variety of coating compositions onto a substrate.
Porous metal abradable seals (also referred to as abradable coatings) may be applied to a substrate by simultaneously plasma spraying metal and polymer particles onto the substrate, generally in accordance with U.S. Pat. No. 3,723,165 to Longo, and copending and commonly assigned U S. Pat. Nos. 4,696,855 to Pettit et al and 4,664,973 to Otfinoski et al, the disclosures of which are all incorporated by reference. For optimum operating characteristics, the abradable coating needs a precisely controlled combination of properties. Tests have indicated that the density and hardness of the coating are among the most important properties, since they correlate well with seal performance during service use.
Accordingly, researchers have expended considerable efforts to develop improved methods for making abradable seals, and to develop methods for measuring the density and hardness of sprayed abradable seals. The present invention satisfies these needs.